Report gives sobering view of warming's impact on US

For anyone wondering whether climate change has already hit the United States, a recent US government report says it has - and in a big way.

Witness these trends: In the northeastern US, winter temperatures have increased by 4 degrees F since 1970; in the Pacific Northwest, the depth of the Cascade Mountain snowpack on April 1 has declined by 25 percent over the last half century, while spring runoff from the Cascades now occurs nearly a month earlier than 50 years ago; and in Alaska, winter temperatures have increased a stunning 6.3 degrees F in the last 50 years.

Those are just some of the sobering signs of rapid warming spelled out this month in a new report by a US government body that almost no one has heard of: the United States Global Change Research Program (USGCR), which by law is required to report to Congress every ten years on the causes, effects, and possible responses to climate change in the US

If the changes that the US already has experienced make you uneasy, then perhaps you shouldn't read the the downloadable document itself: It makes quite clear that if the US and the world do little or nothing to slow greenhouse gas emissions, then the climate in the US will be far hotter - and decidedly unpleasant - by the end of this century.

For those inclined to dismiss the USGCR's report, it should be noted that the group's scientific pedigree is impeccable. The study is a joint effort of the departments of Energy, Commerce, Defense, State, Interior, Transportation, Health and Human Services, and Agriculture - plus the Environmental Protection Agency, NASA, the Smithsonian Institution, the National Science Foundation, and the Agency for International Development.

The report, which includes new material not contained in the 2007 report of the Intergovernmental Panel on Climate Change, brings climate change down to the level where people live. For each region of the US, the report describes some of the changes that have already been observed, then looks at what's likely to happen under both a low-emissions scenario (in which emissions of greenhouse gases are cut substantially) and a high-emissions scenario (where the world pretty much stays on the course it's now following).

Either way, the authors say, significant changes are coming. Substantial emissions cuts are under active debate, but they remain hypothetical so far; the highlights cited here will therefore focus on the business-as-usual scenario - not in order to be alarmist, but to stay in the realm of the concrete. 

NORTHEAST

If emissions continue on their current trajectory, these changes are likely to intensify. Cities like Boston, where 100 degree-plus days are now rare in summer, can expect about 20 of them every year. Cities like Hartford and Philadelphia could have up to 30. The hottest stretch of summer could begin three weeks earlier than it does now, and last three weeks longer in the fall. In winter, the snow season in the mountainous, northern part of the region could be only half as long; partly as a result, droughts lasting from one to three months are likely to occur as often as once a summer in those same areas.

These changes could have a significant impact on regional economies. Dairy farming, for example, is worth $3.6 billion, but the report says heat stress on cows is projected to cut milk production by up to 20 percent by century's end. Areas of the Northeast that now produce apples, blueberries, and cranberries may become inhospitable, and sugar maple habitat may shift so far northward that maple syrup could largely become an imported delicacy. Winter recreation including skiing and snowmobiling, which bring in $7.6 billion annually, could suffer dramatically.